ASP.NET 5 MVC: unable to connect to web server 'IIS Express'

Question

What I'm doing:

• Opening Visual Studio Community 2015
• File -> New -> Project
• Under Visual C#: Web -> ASP.NET Web Application
• Web Application
• And press f5 for the popup error "unable to connect to web server 'IIS Express'."

Deleting applicationhost.config, located in Documents\IISExpress\config, doesn't change the error message. (There's also an IISExpress folder in program files and program files (x86).)

Something I noticed, and I don't know if it's a problem:

Referenced file 'lib/jquery-validation/jquery.validate.js' not found.

I got a dump with rawcap but I don't notice much in there. Some of what was there:

"Framework":{"FrameworkName":"DNXCore,Version=v5.0","FriendlyName":"DNX Core 5.0","ShortName":"dnxcore50","RedistListPath":null}

I don't notice a problem, but I have the network data if that can help figure out why I cannot connect to the web server. I get a RST,ACK immediately so I'm guessing the port is closed and whatever this web server is, isn't being setup.

More on this problem: 800700c1 error from /trace:error

I've tried:

• deleting applicationhost.config (and changing port number)
• running visual studio as administrator
• deleting IISExpress folder in Documents (changes error message until the folder is reinstalled)
• toggling ssl off and on, copying url to launch box. (note: I'm not using ssl)
• clearing all sfc /scannow errors
• starting iisexpress with x86 version and 64-bit version

Answer 1

After installing Update 2 for Visual Studio 2015 I started getting the same error. I tried everything above with no luck. However, I found a solution that works for me:

1. Delete YourSolutionFolder\\.vs\config\applicationhost.config file (note: .vs is a hidden folder)
2. Open Visual Studio, right-click on web site > Properties > Debug tab > Web Server Settings > App URL - change port number.

Answer 2

Exit VS and delete the (project)\.vs\applicationhost.config file. Restart VS. It should start working.

Answer 3

Try using a different port. I just set up a new Core 1.0 RC1 project and got the same error.

• Right click web project
• Debug tab
• Toggle Enable SSL off and on again, it should generate a new random port
• Copy the SSL URL and paste into Launch URL box
• Run the project

Worked for me (TM).

Answer from: https://stackoverflow.com/a/28650554/134761

Answer 4

I had this issue on .net core 2.1, visual studio version 15.9.6. When i deleted the .vs folder, i reopened visual studio and the problem was still there. The solution that worked for me below:

1. Delete .vs folder (it is a hidden folder).
2. Restart Computer.

Other Solutions:

• Close Visual Studio, delete bin and obj folders from the project folder. Open Project then rebuild solution.
• Try running Visual Studio as Administrator.
• Clean Solution then rebuild
• 1. Clean Solution. 2) Exit Visual Studio. 3) delete .vs folder 4) Re-open Visual Studio
• Restart machine (if you can afford to)

Answer 5

I faced this issue in .net core 2.0 when I update my project's port number.

I was able to sort out issue in two steps :

• STEP 1 : DELETE .vs folder which is hidden inside main solution folder. (close visual studio before this) then when you start again visual studio, this folder and file (applicationhost.config) inside it will automatically create by visual studio.
• STEP 2 : For multiple startup projects, if you are still facing issue then one by one run project as startup, and then run as multiple startup project.

Answer 6

Copied my comment to an answer by request.

For Net Core 2.2 project - After a MASSIVE struggle and trying everything from deleting .vs folder, deleting IIS Express configs, changing port numbers, changing bindings, and to running VS as admin I FINALLY fixed issue by

1. closing VS,
2. deleting launchSettings.json
3. opening VS which re-generated launchSettings.json.

It was not apparent that the file was corrupt or incorrect or even when it changed to cause failure.

Answer 7

I had the same issue, i was able to solve it by changing the Port number.

1. Right click on the project and select properties

2. Go to the Debug section

3. Under Web Server Settings change App URL port [just increase by one :)]

Answer 8

Many of these answered don't fully address the issue at hand. The real problem for me was that I had two bindings using the same port in my applicationhost.config file AND I hadn't opened up the port to my second (non localhost) binding. VS will allow you to still run under these circumstances but only if you are in admin mode (hence all of the answers above).

You are essentially creating two IIS express instances of your app on the same port, so changing one of the ports in your applicationhost.config file will allow you to proceed. There are two different applicationhost.config files however. You will want to select the one that has the binding IP and port that you see in your project's properties

.

Go to the folder where you can see your project solution and project folders (show hidden items in File Explorer). Navigate into your hidden .vs folder -> "YourAppName" folder -> config. It should contain the binding info you saw in your project's properties.

Example:

<bindings>
    <binding protocol="http" bindingInformation="*:7000:127.0.0.1" />
    <binding protocol="http" bindingInformation="*:7000:192.168.0.5" />
</bindings>

Change one of those port numbers to something other than "7000" so that you aren't trying to use the same port.

In my case, I'm using a 192 address which is not a localhost address, so I need to use some netsh commands to open that port and ip up. Here is a Link that shows how to open up ports for IIS Express to allow remote connection. Running as a normal user will not work unless you run those netsh commands listed.

Here are the netsh commands:

1. netsh http add urlacl url=http://192.168.1.42:58938/ user=everyone
2. netsh advfirewall firewall add rule name="IISExpressWeb" dir=in protocol=tcp localport=58938 profile=private remoteip=localsubnet action=allow

Copy those commands and run them in cmd with ADMIN privileges and with YOUR ip address and port number.

Answer 9

Run VisualStudio with administrator privilegies and run the project. Then close VisualStudio and all errors and run VisualStudio again with the normal user.

This did it for me.

Looks like that IIS has to write something to some config with admin privilegies (port 80 didn't work with normal user but port 6767 worked fine).

Answer 10

I just changed my profile from "IIS Express" to "MyProjectName" (which I think is using kestrel as the http server instead of IIS) and now it's working fine:

Answer 11

In my case that was some other application listening on the same port which IIS Express trying to attach to. I have to run netstat -ao to see PID of process which is use same port and shutdown application. In my case application was Viber.

Answer 12

The solution that worked for me was to: Close the VS project In File Explorer, navigate to the project and delete the entire ".vs" folder Restart the project Run as "Debug" Works Apparently, it has something to do with the "applicationhost.config" file.

Enjoy!

Answer 13

TO CLARIFY

Really a lot of answers here are the same and say something like "Restart and it magically works again".

Well, 9 out of 10 times people have this issue like the OP it is because THE IP-ADDRESS IS ALREADY IN USE.

ANSWER

There could be 2 ip-addresses that are in use. Both of them you can find by:

1) Right-clicking on the start-up project

2) Click on "Properties"

3) Click on the "Debug" tab

Here you see your "App URL" and your "SSL URL".

• If your "App URL" is in use, just change it there and save it and it should work again.

• If your "SSL URL" is in use, close down VS, delete the "applicationhost.config" file in the hidden .vs folder of your project and open VS up again.

Answer 14

If you can afford to restart your machine then do it 👌, this fixed my issue after almost an hour of trying to fix this issue with no hope 🤯.

Answer 15

I was able to toggle this error by changing a single thing. In my ASP.Net Core 1.0 RC2 Web Application project's launchSettings.json file:

  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "https://localhost:18177/",
      "sslPort": 0
    }
  },

to

  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "http://localhost:18177/",
      "sslPort": 0
    }
  },

I had changed to https in an attempt to run the project using that protocol. Apparently this is not the place to make that change. I suspect it is creating multiple bindings on the same port, and IIS Express doesn't like that.

Answer 16

I had this same issue, but the way I fixed it was by going to the applicationhost.config and remove a port which was not added by me (IIS Express I would guess) which placed my specific port site on another port.

Here is what the config file had for my bindings:

<bindings>
      <binding protocol="http" bindingInformation="*:54764:localhost" />
      <binding protocol="https" bindingInformation="*:44360:localhost" />
</bindings>

I removed the first bindings item as the only port I wanted was 44360. My config file now looks like this:

<bindings>
      <binding protocol="https" bindingInformation="*:44360:localhost" />
</bindings>

Now I don't see the error when I debug.

I also noticed my second API in my project had port 80 also assigned to it, I removed that as well.

Answer 17

delete bin and obj folders from the project folder and rebuild.

Answer 18

I just Cleaned my solution, Then Re-Built it and finally hit F5 and it worked! So simple.

Answer 19

I won't pretend to fully understand what MS bug creates this problem, but here is another potential solution:

In the .vs/config/applicationHost.config file, find the section for <system.applicationHost><applicationPools>. Under the pools, ensure that the managedRuntimeVersion attribute value matches the value which is in the IIS config for the system (and/or the version of the .NET framework which is installed).

For example, you may find (as I did) that the generated file has:

    <add name="Clr4IntegratedAppPool" managedRuntimeVersion="v4.0" managedPipelineMode="Integrated" CLRConfigFile="%IIS_USER_HOME%\config\aspnet.config" autoStart="true" />

In my case, you would replace this with:

    <add name="Clr4IntegratedAppPool" managedRuntimeVersion="v4.0.30319" managedPipelineMode="Integrated" CLRConfigFile="%IIS_USER_HOME%\config\aspnet.config" autoStart="true" />

Note the replacement from "v4.0" to "v4.0.30319". This resolved the issue.

---

What appears to be going on:

I believe that VS is generating an applicationHost.config file with "default" versions for the .NET framework, which may not match the specific version which is installed/configured on the system. You can debug/observe this issue by tracing the execution in Process Monitor, and finding the command line for iisexpress.exe. Running this command with /trace:error added yields a more informative message about a failure to preload the CLR with version v4.0. To wit:

Starting IIS Express ...
Failed while trying to preload CLR version v4.0. hr = 80131700
Failed to initalize the W3WP_HOST hr = 80131700
Process Model Shutdown called
Unable to start iisexpress.

---

Anyway, figured this might be helpful to someone else, since it's common enough to have multiple references online with bad information, and I've personally hit it a few times now.

Answer 20

For me the problem was that an other process was using the same port. (In my case it was outlook that was using the same port as my site and thus my site couldn't start)

Yes you can change the local port, but if you are running an API or something that other applications need, you don't always want to do this.

To get a list of what applications are using what port open CMD and type "netstat -aon" You will get a list of ports. Find the port that your site should use, or that you want to use and write down / remember the PID.

Now open task manager and click on the tab 'details'. Find the process with your PID and end it. Now you should be able to start IIS Express with that port.

Answer 21

For me, IIS Express was not accessible when I added iplisten on DOS Prompt like this: netsh http add iplisten MyIPAddress. I fixed it by deleting the iplisten like this: netsh http delete iplisten MyIPAddress.

Answer 22

I just encountered the same problem and I killed all the "iisexpress.exe" processes that were still running. That worked for me!

Answer 23

Try this first if it was working and suddenly stopped:

• Close Visual Studio
• Kill iisexpress.exe processes
• Reopen Visual Studio

Answer 24

Mine happens as soon as I add a new binding inside the applicationhost.config, running as administrator fixed the problem.

Answer 25

Just close the visual studio and reopen and execute. It worked for me.

Answer 26

My solution (for .net core 2.0) was that i had forgot to add the port number in the applicationUrl, under iisExpress in launchSettings.json

"iisExpress": {
  "applicationUrl": "https://localhost:50770",
  "sslPort": 50770
}

Answer 27

I was able to resolve this by restarting my computer. I tried a few things unsuccessfully and finally gave up and restarted my computer. It has been working well now for a couple of days after I restarted. Probably the result of some process that was hung.

Answer 28

For me, it was a mixture of following these instructions:

Delete your web application’s .vs\applicationhost.config and try again.

And then, perhaps most importantly, running Visual Studio with admin privileges.

Answer 29

I added .UseUrls("https://localhost:<some port>/") to the Program.cs. This seemed to do the trick for me!

Answer 30

The issue may be because [√] Enabled SSL was selected for your project (see the Debug tab in the project settings window), but Visual Studio decides to be dumb and setup something like http://localhost:32396. The reason it fails is because 1. it is not HTTPS, and 2. the cert is not valid. To force it, you need to use a port in the range 44300-44398.

See https://stackoverflow.com/a/24957146/1236397